Preparation of nitrones

ABSTRACT

A method for producing a nitrone of formula (I) 
     
       
         
         
             
             
         
       
     
     wherein R is a branched alkyl group having from four to thirty carbon atoms; R 1 , R 2 , R 3  and R 4  independently are hydrogen or alkyl groups having from one to six carbon atoms from an imine having formula (II)

This invention relates to a method for preparation of aromatic nitronecompounds, and to a method for use of the nitrone compounds as fuel andoil stabilizers.

Nitrones have been prepared by a variety of methods. For example, U.S.Pat. No. 5,527,828 discloses aromatic nitrones produced by condensationof alkylhydroxylamines with benzaldehydes. However, mostalkylhydroxylamines are not available commercially, and must besynthesized in a separate step.

The problem addressed by this invention is to find an alternativepreparation of nitrones.

STATEMENT OF INVENTION

The present invention provides a method for producing a nitrone offormula (I)

wherein R is a branched alkyl group having from four to thirty carbonatoms; R¹, R², R³ and R⁴ independently are hydrogen or alkyl groupshaving from one to six carbon atoms; said method comprising treating animine having formula (II)

with a peroxy acid.

The present invention further provides a method for stabilizing fuel orlubricating oil by adding 0.01 to 5 wt % of the nitrone of formula (I).

The present invention further provides novel compounds of formula (I) inwhich R is tertiary and has from nine to thirty carbon atoms.

DETAILED DESCRIPTION

Percentages are weight percentages (“wt %”) and temperatures are in °C., unless specified otherwise. An “alkyl” group is a saturatedhydrocarbyl group having from one to thirty carbon atoms in a linear,branched or cyclic arrangement. A “peroxy acid” is an organic compoundhaving a peroxy carboxylic acid group, C(O)OOH. Preferably, a peroxyacid is an aromatic peroxy acid, more preferably peroxybenzoic acid or asubstituted (e.g., alkyl, nitro, alkoxy, halo) peroxybenzoic acid, andmost preferably meta-chloroperoxybenzoic acid (“MCPBA”). A “fuel” is anysubstance burned in an internal combustion engine or heating furnace,including, e.g., gasoline, kerosene, diesel fuel, jet fuel, biodieselfuel, fuel oil, and bunker C fuel (number 6 fuel oil for marineapplications).

The imine of formula (II) may be prepared and isolated prior totreatment with peroxy acid, or the imine may be formed and treated withperoxy acid without isolation. The imine typically is prepared from3,5,-di-tert-butyl-4-hydroxybenzaldehyde and an amine RNH₂, althoughother preparations of imines are known in the art.

In some embodiments of the invention, the branched alkyl group R is atertiary alkyl group. In some embodiments, the tertiary alkyl group isderived from one or more of the PRIMENE™ amines available from Rohm andHaas Company; Philadelphia, Pa. For example, an isomeric mixture of C₁₆to C₂₂ tertiary alkyl primary amines (PRIMENE JM-T amine); an isomericmixture of C₈ to C₁₀ tertiary alkyl primary amines (PRIMENE BC-9 amine);an isomeric mixture of C₁₀ to C₁₅ tertiary alkyl primary amines (PRIMENE81-R amine); or mixtures thereof. In some embodiments, the amine is adiamine in which each amino group is attached to a tertiary alkyl group.An example of such an amine is PRIMENE MD amine, available from Rohm andHaas Company; Philadelphia, Pa. In these embodiments, preferably thePRIMENE amine is condensed with the corresponding substitutedbenzaldehyde to produce imine (II).

In some embodiments of the invention, the branched alkyl group R isderived from a cyclic or polycyclic amine having from six to twentycarbon atoms, alternatively from eight to sixteen carbon atoms. In someembodiments, R is tertiary alkyl. Examples of suitable cyclic orpolycyclic amines include 1-aminoadamantane and PRIMENE MD amine.

In some embodiments of the invention, the branched alkyl group R has atleast six carbon atoms, alternatively at least eight carbon atoms. Insome embodiments, the branched alkyl group R is tertiary, and has fromeight to twenty-two carbon atoms, alternatively from eight to sixteencarbon atoms, although small amounts, i.e., less than 1% of larger alkylgroups are permitted in either case. For example, PRIMENE amines containsmall amounts of larger alkyl groups.

In some embodiments of the invention, R¹, R², R³ and R⁴ are alkyl groupshaving from one to four carbon atoms. In some aspects of theseembodiments, R³ and R⁴ are alkyl groups having from one to four carbonatoms and R¹ and R² are hydrogen or methyl; alternatively, R³ and R⁴ arealkyl groups having from one to four carbon atoms and R¹ and R² arehydrogen; alternatively, R³ and R⁴ are tert-butyl and R¹ and R² arehydrogen or methyl; alternatively R³ and R⁴ are tert-butyl and R¹ and R²are hydrogen. A particularly preferred nitrone has formula (III):

In some embodiments of the invention, the nitrone is prepared from thecorresponding substituted benzaldehyde, e.g.,3,5-di-tert-butyl-4-hydroxybenzaldehyde, without isolation of the imine.In these embodiments, the benzaldehyde and the amine, RNH₂ arecontacted, and water is removed, preferably by distillation or by use ofa dehydrating agent. Peroxy acid is then combined with the resultingimine solution.

In some embodiments of the invention, the imine is combined with theperoxy acid at a temperature from −30° C. to 20° C. In some embodiments,the temperature is no more than 15° C., alternatively no more than 10°C., alternatively no more than 5° C. In some embodiments, thetemperature is at least −20° C., alternatively at least −10° C.Preferably, the reaction mixture is kept in this temperature range forat least 30 minutes after the imine and peroxy acid are combined,alternatively at least 60 minutes, alternatively at least 2 hours. Afterthis time, the temperature of the reaction mixture typically is raisedto at least 10° C., alternatively at least 15° C.; but no more than 30°C., alternatively no more than 25° C. Preferably, the reaction mixtureis maintained in this higher temperature range for at least 1 hour,alternatively at least 2 hours, alternatively at least 4 hours.

The solvent for the reaction may be any solvent in which the imine andthe peroxy acid are soluble, and which does not react significantly withthe peroxy acid. For example, suitable solvents include methylenechloride, ethyl acetate, methyl acetate, t-butanol, diethyl ether,ethanol and chloroform. Ethyl acetate is preferred.

In embodiments of the invention in which the nitrone of formula (I) isadded to lubricating oil or fuel as a stabilizer, preferably the amountof nitrone added is at least 0.001%, alternatively at least 0.01%,alternatively at least 0.05 wt %, alternatively at least 0.1 wt %,alternatively at least 0.2 wt %. Preferably, the amount of nitrone is nogreater than 3 wt %, alternatively no greater than 2 wt %, alternativelyno greater than 1 wt %, alternatively no greater than 0.5 wt %. Otheradditives that could be used in combination with the nitrone of formula(I) include ZDDP (zinc dithio dialkyl phosphates), octylated orbutylated diphenylamines, and hindered phenols.

EXAMPLES Example 1 Preparation of 2,6-di-tert-butyl-4-(N-tert-octyl)nitronyl phenol (DBONP) with Isolation of Imine (a) Preparation of2,6-di-tert-butyl-4-((2,4,4-trimethylpentan-2-ylimino)methyl)phenol

To a nitrogen-charged 250 mL, 4-necked round bottom flask equipped witha TEFLON-coated magnetic stirrer, a thermometer, nitrogen gas flow,addition funnel, and a Dean-Stark apparatus equipped with a condenserand a receiver was added 9.8590 g (0.042 moles) of3,5,-di-t-butyl-4-hydroxybenzaldehyde followed by 100 mL of toluene withvigorous stirring. The solution was not clear and the aldehyde was notsoluble in toluene at room temperature. 5.8 gm of t-octylamine was addedinto the reaction via addition funnel. The reaction flask was slowlyheated to 60° C. by heating mantle, and the temperature was controlledby a THERM-O-WATCH® Controller/Monitor. The solution became clear darkreddish brown. The reaction was monitored for 2 hours at 60° C. by ThinLayer Chromatography (TLC). Then the temperature was raised to 110° C.to remove the water by azeotrope with toluene. The azeotrope of waterand toluene was collected in a receiver attached to Dean-Stark. Afterthe calculated amount of water was removed, the reaction was cooled toroom temperature. The completion of the reaction was monitored by InfraRed Spectroscopy (IR) analysis and by the amount of water collected inthe Dean-Stark receiver. The IR analysis confirmed the disappearance ofwave number 1682 cm⁻¹ (aldehyde C═O) and appearance of wave number 1621cm⁻¹ (imine C═N). The imine was collected by evaporating toluene using arotary evaporator under water aspiration with 94.48% yield.

(b) Preparation of 2,6-di-tert-butyl-4-(N-tert-octyl) nitronyl phenol(DBONP)

13.7 g of (0.0396 moles) of2,6-di-tert-butyl-4-((2,4,4-trimethylpentan-2-ylimino)methyl)phenol frompart (a) was added to a 500 mL 3-neck round bottom flask equipped with athermometer, a condenser, and an addition feed funnel withpressure-equalization arm. 100 mL methylene chloride was added in to theflask to dissolve the imine. A solution of 10.18 g of purifiedmeta-chloroperoxybenzoic acid (commercially available MCPBA typically is70 to 77% pure. The impurity is m-chlorobenzoic acid, which is moreacidic than the peracid. MCPBA is thus purified by washing with aphosphate buffer of pH 7.5 and drying at reduced pressure.) in 100 mL ofethyl acetate was made in a beaker and transferred in to the feedfunnel. The reaction flask was cooled to 0° C. using ice bath. Once thetemperature reached 0° C., the solution of MCPBA from the feed funnelwas fed in to the reaction flask slowly over a 45 to 60 minute period,while maintaining the temperature at 0° C. The reaction mixture turnedinitially bluish in color and eventually changed to green. The reactionmixture was held for 2 hours at 0° C. and then slowly allowed to warm toroom temperature. The reaction mixture was transferred to a 1-literseparatory funnel. The mixture was then washed twice with 100 mL of 7%NaHCO₃ solution followed by water wash 2×100 mL each. Then the mixturewas washed twice with 100 mL of saturated sodium chloride solution, thenwith 2×100 mL water. The mixture was then dried overnight using Na₂SO₄or MgSO₄. The crude nitrone then was concentrated using a rotaryevaporator. The nitrone is purified using flash chromatography columnusing silica gel (66A°), and product eluted with mixture of hexane/ethylacetate (“EtOAc”) (70:30) to give 13.56 gm of yellowish color solidcrystals. The final product was recrystallized with pentane to give 12.1gm of off-white crystalline solids. The melting point was 150-155° C.

Example 2 Preparation of (DBONP) without Isolation of Imine

To a nitrogen charged 250 mL, 4-necked round bottom flask equipped witha Teflon coated magnetic stirrer, a thermometer, nitrogen gas flow,addition funnel, and a Dean-Stark apparatus equipped with a condenserand a receiver was added 9.8590 gm (0.042 moles) of3,5,-di-t-butyl-4-hydroxybenzaldehyde followed by 100 mL of toluene withvigorous stirring. The solution was not clear and the aldehyde was notsoluble in toluene at room temperature. 5.8 gm of t-octylamine was addedinto the reaction via addition funnel. The reaction flask was slowlyheated to 60° C. by heating mantle, and the temperature was controlledby a THERM-O-WATCH® Controller/Monitor. The solution became clear darkreddish brown. The reaction was monitored for 2 hours at 60° C. by ThinLayer Chromatography (TLC). Then the temperature was raised to 110° C.to remove the water by azeotrope with toluene. The azeotrope of waterand toluene was collected in a receiver attached to a Dean-Starkapparatus. After the calculated amount of water was removed, thereaction was cooled to room temperature. The completion of the reactionwas monitored by Infra Red Spectroscopy (IR) analysis and by the amountof water collected in the Dean-Stark receiver. The IR analysis confirmedthe disappearance of wave number 1682 cm⁻¹ (aldehyde C═O) and appearanceof wave number 1621 cm⁻¹ (imine C═N). The Dean-Stark apparatus, thecondenser, and the receiver were removed. An addition funnel withpressure-equalization arm was attached to the reaction flask. A solutionof 10.18 gm of purified MCPBA in 100 mL of ethyl acetate was made in abeaker and transferred in to the addition funnel. The reaction flask wascooled to 0° C. using ice bath. Once the temperature reached 0° C., thesolution of MCPBA from the feed funnel was fed in to the reaction flaskslowly over a 45 to 60 minute period, while maintaining the temperatureat 0° C. The reaction mixture turned initially milky bluish color andeventually changed to milky green. The reaction mixture was held for 2hours at 0° C. and then slowly allowed to warm to room temperature. Thereaction mixture turned clear green at room temperature. The reactionmixture was stirred for an additional 2 to 8 hr at room temperature. Thereaction mixture was transferred to a 1-liter separatory funnel. Themixture was then washed twice with 100 mL of 7% NaHCO₃ solution, thenwith 2×100 mL water. Then the mixture was washed twice with 100 mL ofsaturated sodium chloride solution followed by wash with 2×100 mL water.The mixture was then dried over Na₂SO₄ or MgSO₄. The crude nitrone thenwas concentrated using a rotary evaporator. Analysis of the crudenitrone by ¹H NMR did not detect any oxaziridine byproduct. The nitronewas purified using flash chromatography column using silica gel (66A°),and product eluted with mixture of hexane/EtOAc (70:30) to give 13.56 gmof yellowish color solid crystals. The final product was recrystallizedwith pentane to give 12.1 gm of off-white crystalline solids. Themelting point was 150-155° C. Anti-oxidancy properties were evaluated byESR technique and compared with PBN (phenyl t-butyl nitrone). The datashowed that the nitrone made from tert-octylamine and3,5-di-t-butyl-4-hydroxy benzaldehyde (Ex. 2) and the nitrone made fromtert-butylamine and 3,5-di-t-butyl-4-hydroxy benzaldehyde (Ex. 3) showedbetter efficiency compared to PBN as shown in Table 1 below:

TABLE 1 Com- parison Regression with Nitrone Rate constant, kcoefficient Concentration, c PBN PBN 4.47 * 10⁹ M⁻¹* s⁻¹ 0.8624 <0.07 mM1 Ex. 2 9.79 * 10⁹ M⁻¹* s⁻¹ 0.944 0.005-0.05 mM 2.19 Ex. 3 7.65 * 10⁹M⁻¹* s⁻¹ 0.8667 0.005-0.05 mM 1.71

The above data clearly indicate that the nitrone made from t-octylamineand 3,5-di-t-butyl-4-hydroxybenzaldehyde following the synthesis routementioned above, is better compared to PBN in terms of scavenginghydroxyl radical.

Two additional nitrones were made using the procedure of Example 2, withPRIMENE 81-R amine (Ex. 4) or PRIMENE JM-T amine (Ex. 5). Thesenitrones, along with the one of Ex. 2 and PBN, were tested in base oilfor antioxidancy according to ASTM procedure E 2009. The results foroxidation onset temperature (“OOT”) are presented below in Table 2.

TABLE 2 Nitrone % in oil OOT (° C.) none 0 195 PBN 0.5 197 Ex. 2 0.5 227Ex. 4 0.5 220 Ex. 5 0.5 203 PBN 0.25 196.5 Ex. 2 0.25 223 Ex. 4 0.25216.4 Ex. 5 0.25 204.5

Nitrones from Ex 2, 4, and 5 along with PBN and antioxidant (mixture ofMono-, Di-, and Tri-tert-butylphenol) were tested in B-100 biodieselfuel (100% biodiesel fuel, ASTM D 6751) for antioxidancy according tothe European EN 14112 test procedure. The results for induction periodin hours (h) at 110° C. are presented in Table 3.

TABLE 3 Induction Period @ Nitrone % in B-100 110° C. (h) none 0 1.93mixture of Mono-, Di-, and 0.01 9.57 Tri-tert-butylphenol Ex 2 0.01 >17Ex 4 0.01 12.15 Ex 5 0.01 8.53 PBN 0.01 0.9 mixture of Mono-, Di-, and0.005 6.81 Tri-tert-butylphenol Ex 2 0.005 9.1 Ex 4 0.0042 7.96 Ex 50.0042 6.8 PBN 0.005 2.02

1. A method for stabilizing fuel or lubricating oil; said methodcomprising adding 0.001 to 5 wt % of a nitrone having formula (I)

wherein R is a branched alkyl group having from four to thirty carbonatoms; and R¹, R², R³ and R⁴ independently are hydrogen or alkyl groupshaving from one to six carbon atoms.
 2. The method of claim 1 in which Ris tertiary and has from eight to twenty-two carbon atoms.
 3. The methodof claim 2 in which R is tert-octyl; and R¹, R², R³ and R⁴ independentlyare hydrogen or alkyl groups having from one to four